Sexual dimorphism in glioblastoma: an interview with Justin Lathia

Justin Lathia is an Associate Professor in the Department of Cellular and Molecular Medicine at Cleveland Clinic Lerner Research Institute (OH, USA). He also leads a translational cancer stem cell research laboratory, which focuses on how the stem cell state is regulated in advanced cancers. Projects in the Lathia laboratory involve understanding how cancer stem cells interact with their surrounding environment as well as one another, with the goal of identifying unique pathways for therapeutic development.

In this interview, Justin speaks to us about his talk on sex differences in microglia and the glioma environment, including how our understanding of this concept has changed in glioblastoma and what advancements we have seen over the last few years. He also discusses what challenges are present within this field of research and how they could be overcome.

1. You attended the 23rd Society for NeuroOncology Annual Meeting (15–18 November 2018, New Orleans, LA, USA). What have been your favorite talks at the meeting and which developments are you most excited about in the field of neuro-oncology?

“…it’s very clear that standard conventional checkpoint inhibitors are probably not going to work.”

There isn’t one single talk that I can point out that stood out the most but I will tell you that there were a lot of larger-scale presentations that specifically dealt with immunotherapy, and I think that’s what really got me excited. There were a few preclinical and clinical talks from people such as Tim Cloughesy at University of California, Los Angeles (CA, USA) and John Sampson at Duke University (NC, USA). I think each of those really highlighted the progress we’ve made in immunotherapy in glioblastoma so far and where things are likely to be moving forwards.

There are always a couple of really elegant talks that are based on screening, which can identify a candidate that is then validated by shRNA and then transitioned into pharmaceutical or pharmacological inhibition. I think this was the main thing, as it’s very clear that standard conventional checkpoint inhibitors are probably not going to work. So whether it’s starting preclinically to think about novel areas, or clinically to think about difference approaches, that’s really the takeaway that I got.

2. You also presented a talk at the meeting on ‘Sex differences in microglia and the glioma microenvironment’ – could you provide us with an overview about this?

This has been something that we’ve been thinking about for a while now and it’s always been there, believe it or not. People have known for some time that the incidence of glioblastoma in males to females is 1.6:1, so there’s a sexual dimorphism present. It turns out that if you adjust for all clinical parameters, males still do worse. Thus, there must be an underlying fundamental sex difference, which has been largely ignored for a variety of reasons that I’ll get into shortly.

We’ve been interested in how cells interact with their microenvironment through adhesion mechanisms and we have identified a sexual dimorphic phenotype in an adhesion molecule termed, JAM-A (also known as F11R or CD321). This is expressed on microglia and for some reason in the JAM-A microglia knockout mice, they exhibit a different phenotype between males and females. It turns out that the female microglia are more hyperactive and drive tumor growth through a variety of mechanisms. Those are the data we presented but we presented it as a larger consortium on sex differences in glioblastoma that was highlighting work from epidemiologists, people who study imaging, and cell and molecular biologists like myself. So it was really all part of a mini-symposium in the morning.

3. As you mentioned just now, it’s been known for a few years that sex differences are present in glioblastoma. How has our understanding of this concept changed and what advancements have you seen over the last few years?

“If you go back to really fundamental biology in terms of transformation assays, where you activate an oncogenic pathway or take out the tumor suppressor pathway at the same time, it’s more difficult to transform a female astrocyte than it is a male astrocyte.”

I believe advancements are really coming on multiple fronts. I think it’s finally being acknowledged that there is a fundamental sex difference between males and females that is likely to be underlying the pathology of glioblastoma. For example, the male and female immune systems are slightly different. They have the same types of cells and they have the same functions but in general, females are more prone to autoimmune diseases and that may be the reason that they don’t develop glioblastoma as frequently, or when they do, they have a better prognosis.

In terms of the concept changing, I believe there’s a lot of work being done right now to determine that male and female glioblastoma cells in experimental models are fundamentally different. They rely on completely different cell signaling programs and the types of mutations that are present within them are actually quite different. If you go back to really fundamental biology in terms of transformation assays, where you activate an oncogenic pathway or take out the tumor suppressor pathway at the same time, it’s more difficult to transform a female astrocyte than it is a male astrocyte.

This is all pointing towards the same concept that there is a fundamental biology here that has to be considered. There is a lot of unpublished work in this area that should be coming out relatively soon but even things as foundational as different drugs will elicit a different response in males and females, and this is the case in glioblastoma cells. They respond differently to drugs depending on sex.

I think this in itself is a complete game changer as it means we’re treating patients irrespective of whether they’re going to respond to the drug or not when actually we may have a better drug.

4. What are the challenges involved with researching sexual differences in microglia and the glioma microenvironment?

“I think as a whole, changing the conversation around glioblastoma as a field to include sex differences has been a little more of a challenge than I anticipated.”

The main challenge is probably trying to model what we see in mice directly into humans. However, we are doing this in a couple of ways already. We have mouse models and we’re validating hypotheses in human samples, but I think the challenge is that frankly, we’re going to be able to understand a lot of things but the question is can we actually target them? I think this is going to be the biggest challenge. It’s great to understand the underlying mechanisms but whether these will actually translated into therapy is something I don’t know. This still remains to be determined. Can we develop drugs specifically against microglia?

I think as a whole, changing the conversation around glioblastoma as a field to include sex differences has been a little more of a challenge than I anticipated. Just the response we sometimes get when we talk about this topic, People are less skeptical than they used to be, more data is coming out and people are a little more accepting of it, but I feel like we are still engaged in an uphill battle.

5. How could these challenges be overcome?

I think that having more studies come out and having more research being done that’s focused on this area is the main thing. To have people understand that there are difference present and that it’s more complicated than this.

For example, the models we use are quite old and it turns out that they have an incomplete suite of sex chromosomes. Right now we are struggling to figure out whether these cells came from a male or female because one of the first things that happens as a cancer cell expands and becomes more tumorigenic and more malignant, is that it basically jettisons its sex chromosomes. So it’s really kind of difficult to identify which sex the original cell came from.

6. What further investigations do you have planned for this area of research?

“We’re looking at every level possible, from the genetic and epigenetic levels, up to the model level to really try to understand where these differences are.“

We’re part of a larger team that consists of people from across the USA. There are approximately 5–7 labs that are trying to work together to do this and we are all pulling our respective expertise and hitting this with as much as we can right now in terms of different mouse models of glioblastoma, different characterization techniques – whether its single-cell RNA sequencing or looking at the epigenetics. We’re looking at every level possible, from the genetic and epigenetic levels, up to the model level to really try to understand where these differences are. Once we have them, we can then try to think about developing therapeutic regimens that are more sex specific.

7. Lastly, where do you anticipate the field will be in the next 5–10 years’ time?

It would really be my hope that the sex of the patient is one of the first things that is considered, not only in diagnosis in terms of looking at their tumor on an MRI, but also in terms of what kind of therapy they would receive and what clinical trials they would be offered. It would be my hope and desire that 5–10 years from now, not every patient is going to get the same standard of care. Additionally, I would love to see the standard of care change based on the patient’s sex.

8. Is there anything more you would like to add?

“…microglia are a cell type in the brain that has demonstrated sexual dimorphism in a variety of diseases from multiple sclerosis to stroke. Therefore, it’s almost obvious that there would be a difference in glioblastoma.”

I would like to highlight that this has been such an important and fundamental area that has been largely overlooked, and I would say that even within our own laboratories, the only reason we started looking into this more carefully is because the NIH actually mandated that we use male and female models of the disease. This then started a series of enquiries for us, where we quickly realized that there was a sexual dimorphism not only in incidence but also survival.

As you dig deep into the literature you realize that microglia are a cell type in the brain that has demonstrated sexual dimorphism in a variety of diseases from multiple sclerosis to stroke. Therefore, it’s almost obvious that there would be a difference in glioblastoma. I guess we have been a little slow in appreciating how fundamental sex differences are in glioblastoma.